Alignment and marking of surfaces is a perennial problem in a variety of fields, ranging from construction to interior decorating. Alignment and marking of height references are necessary for walls that should be perpendicular to a floor, or otherwise plumb. Masonry and brick-laying practitioners are well aware of the importance of plumbed and aligned surfaces and chalk lines. Especially for internal finishing works, e.g. the installation of power outlets or furniture, it is often required to place several marks onto a wall, the marks each having equal heights and, thus, being on-grade with respect to each other. Furthermore, a home interior decorated with pictures and other wall ornamentation makes a much better appearance when the ornamentation is horizontally aligned and on-grade with respect to each other.
Many mechanical and electrical alignment and height measurement devices as well as numerous laser devices are available. Some of these products are cumbersome and others are not suitable for certain uses. Chalk lines, for instance, are disadvantageous for use in finished interior areas and for precisely referencing a desired predefined height.
Typical laser devices used for marking a true horizontal line and/or for precisely indicating a reference height are rotating construction lasers. The design of rotating lasers—and also of auto-leveling rotating construction lasers—is well known to persons skilled in the art. U.S. Pat. No. 4,062,634, issued Dec. 13, 1977, to Rando, illustrates a laser transmitter which provides such a rotating reference beam. The rotating beam defines a plane, and various measurements can be made using the plane as a reference. The reference plane may be horizontal or inclined. In particular, such devices allow construction workers to quickly lay out visible marking-lines or adjust heights by eye.
However, a conventional rotating laser generator is not well-equipped for projecting a flat or planar beam of light. Due to eye safety regulations, visible rotating construction lasers must have low power beams.
Hence, rotating construction lasers are—on the one hand—able to indicate a precise reference height. However—on the other hand—the width, brightness and straightness of the projected laser light are insufficient for many applications. The projected, visible laser line may be limited in its brightness over a distance, and also tends to defocus and become dimmer as a user works away from the source of the laser.
When rotating, the maximum realistic visual operating range of the laser—dependent on light conditions—is 10-20 meters from the rotating laser unit. Past this distance, the laser plane is both too wide to precisely locate its center due to the divergence of the rotating laser beam and not adequately bright to see with the naked eye. The user must either use a hand-held laser receiver to find the laser beam, and no longer work visually, or tear down the laser setup and move it closer to the desired work location. Both of these options are cumbersome and time consuming.
Another aspect that could be improved is the inability of laser devices to work around obstructions. That is, if a piece of furniture interrupts the laser beam, it may be blocked from further projection. Therefore, it is necessary to mark locations or heights, one by one, rather than working with the actual objects, in order to align them. Obstructions may include furniture, the operator of the device, moldings placed in a doorway, an interior wall or other obstacles.
As indicated above, one possibility in order to precisely transfer a reference height indicated by a laser plane of a rotating device is to use a hand-held laser receiver. Laser receivers allow for finding and sighting the rotating beam and marking corresponding locations on the wall adjacent to the laser receiver. Therefore, the operator moves the laser receiver in vertical direction to a position where it intercepts the laser beam, as indicated by a display on the receiver. One such laser receiver is shown in U.S. Pat. No. 4,240,208, issued Jun. 30, 1987, to Pehrson.
Conventional laser receivers are small hand-held devices which include a display and a laser light photo sensor. The photo sensor typically comprises a plurality of photo sensitive elements providing an electrical output when illuminated by the laser beam of a rotating laser. Particularly, the photo sensitive elements are arranged in a generally vertically oriented row.
Most laser detectors or receiver devices have included circuitry that provides an indication of the position of the detected reference light with respect to the device as a ratio between several output signals.
Especially, the circuitry is connected to the photo sensor and designed for determination—based upon the outputs of the photo sensitive elements—of a vertical offset between the receiver and the detected vertical center of the rotating beam. The receiver is moved by the operator until it indicates that it is on-grade with respect to the rotating laser beam. Particularly, the laser receiver has a defined zero-point, e.g. the center of the photo sensor—which has to be brought on-grade—that means on equal height—with respect to the vertical center of the detected rotating beam.
In order to allow an operator to transfer with high precision the detected height reference of the rotating beam onto a target surface like a wall, the laser receiver may comprise a height mark on the left or right side of the receiver housing.
However, when using such laser receivers, it is necessary to mark locations or heights, one by one, and, therefore, to have the receiver resting in hand during the pointwise transformation of the reference height onto the wall. Moreover, the wall itself requires marking with this method.